SPERMATOGENESIS OF SQUILLA ORATORIA 319 
and 42). Rarely, this division of the centrosome is completed 
before any trace of vacuole can be detected in the cytoplasm 
(fig. 41). 
The nucleus next undergoes an important change, both in 
shape and in consistency. - To this time the nucleus has been 
hemispherical in shape, granular in consistency, and stained 
very heavily with iron-hematoxylin quite dark, but it now 
becomes ovoid (figs. 43 and 44) and then hemispherical, but 
with its flat surface away from the center of the cell, contrary 
to the initial state (figs. 42, 47 to 51). It becomes, moreover, 
quite homogeneous in consistency and stains with iron-hema- 
toxylin a tawny color, save the marginal part which is still 
dark (figs. 46, 49 to 51). This change of consistency advances 
from the peripheral part centrad, as is clearly shown in figure 
43, in which the central region of the nucleus is still dark and 
granular, while the marginal part has already become homo- 
geneous. The nucleus in the meantime comes into intimate 
contact with the cell wall adjacent to it, where a low conical 
prominence develops from the nucleus, presenting a granular 
appearance, especially in its basal part (figs. 44, 47 to 51 p). 
Without doubt, this prominence represents the perforatorium. 
But it is somewhat doubtful if it does develop actually from the 
nucleus, inasmuch as there is possibility of the cytoplasm 
taking part of its formation. Since the prominence arises where 
the nucleus is in intimate association with the cell wall, it is not 
easy to ascertain the fact definitely. For the present,  fter 
having gone over tolerably many preparations, I am inclined to 
claim the nuclear origin of it. 
Just before this change of the nucleus, one of the two centro- 
somes elongates to assume a rod-shape and takes the position of 
the axis of the perforatorium (figs. 47 to 51, c.1). The clear 
space around that centrosome is not infrequently discernible 
after the transformation (figs. 49 and 50), but later it appears 
to fade away. Figures 44 and 45 illustrate the change of the 
centrosome just mentioned. In figure 44 the centrosome is in 
the course of transformation at the distal extremity of the 
nucleus, which is ovoid in shape; around the two centrosomes is a 
